This invention relates to an information recording and reproducing apparatus of the type which utilizes an information storing medium capable of recording information in response to a laser beam and relates in particular to an information recording apparatus for improving the error rate of dissimilar optical disks.
A method of tracking while passing a laser beam over an address information region when scanning the track of an optical recording medium having track address information at a position deviated from the track center is disclosed in Japanese Published Unexamined Patent Application Hei 7-272297.
In the next generation of recording mediums, such as a DVD-RAM having 4.7 gigabtyes of information on one side of a disk 120 millimeters in diameter, the information track pitch is less than one-half the diameter of the laser spot. When recording on an information track, however, a cross-erase phenomenon occurs, causing deterioration of data on adjacent tracks. The cross-erase phenomenon results from heat propagating to adjacent tracks during recording and crystallizing a portion of the amorphous marks formed on adjacent tracks. Offsets in the laser beam scanning position of the laser beam become substantial due to the cross-erase phenomenon. Therefore, in order to minimize the occurrence of this cross-erase phenomenon, the marks must be correctly formed at the center of the information track.
The optical disk recording medium, however, uses a plastic substrate so that slack or stretching radially along the disk is unavoidable due to stress and changes which occur over time. The disk at this time develops a radial tilt relative to the center axis of the laser beam. In tracking control typically using the push-pull method, an offset is issued from a track detection signal relative to the radial tilt. The radial tilt must be maintained within a fixed amount in order to ensure compatibility with other optical disks.
In view of the problems in the prior art due to cross-erase and radial tilt on high density optical disks and the need for optimal track control conditions during recording and reproduction, this invention therefore has the object of providing an information recording and reproducing apparatus that prevents cross-erase during recording and also improves the reproduced signal that is susceptible to deterioration accompanying the occurrence of radial tilt.
To achieve the above described objects of the invention and eliminate the problems in the prior art, the information recording and reproducing apparatus is configured as follows.
Firstly, an information recording and reproducing apparatus for scanning with a laser beam along an information track and recording and reproducing information is comprised of a tracking servo circuit which operates to position said information tracking laser beam; a track center detector circuit which operates to detect deviations between the scanning position of the laser beam and the center of the information track; a track center compensator circuit for supplying a track offset signal obtained from the track center detector circuit to the tracking servo circuit, to offset (correct) the scanning position of the laser beam; and a switching circuit to selectively control the supply of the track offset signal to the track offset circuit, which switching circuit is switched on and off depending on the operations being performed.
Secondly, the information recording and reproducing apparatus is characterized by the fact that the switching circuit is turned on when the apparatus is recording information.
Thirdly, the information recording and reproducing apparatus is characterized by the fact that the switching circuit is turned off when a data error has occurred during reproduction of information.